/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core.convert.support;

import org.springframework.core.convert.ConversionService;
import org.springframework.core.convert.TypeDescriptor;
import org.springframework.core.convert.converter.ConditionalGenericConverter;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

import java.lang.reflect.Array;
import java.util.Collection;
import java.util.Collections;
import java.util.Set;

/**
 * Converts a Collection to an array.
 *
 * <p>First, creates a new array of the requested targetType with a length equal to the
 * size of the source Collection. Then sets each collection element into the array.
 * Will perform an element conversion from the collection's parameterized type to the
 * array's component type if necessary.
 *
 * @author Keith Donald
 * @author Juergen Hoeller
 * @since 3.0
 */
final class CollectionToArrayConverter implements ConditionalGenericConverter
{

    private final ConversionService conversionService;


    public CollectionToArrayConverter(ConversionService conversionService)
    {
        this.conversionService = conversionService;
    }


    @Override
    public Set<ConvertiblePair> getConvertibleTypes()
    {
        return Collections.singleton(new ConvertiblePair(Collection.class, Object[].class));
    }

    @Override
    public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType)
    {
        return ConversionUtils.canConvertElements(sourceType.getElementTypeDescriptor(), targetType.getElementTypeDescriptor(), this.conversionService);
    }

    @Override
    @Nullable
    public Object convert(@Nullable Object source, TypeDescriptor sourceType, TypeDescriptor targetType)
    {
        if (source == null)
        {
            return null;
        }
        Collection<?>  sourceCollection  = (Collection<?>) source;
        TypeDescriptor targetElementType = targetType.getElementTypeDescriptor();
        Assert.state(targetElementType != null, "No target element type");
        Object array = Array.newInstance(targetElementType.getType(), sourceCollection.size());
        int    i     = 0;
        for (Object sourceElement : sourceCollection)
        {
            Object targetElement = this.conversionService.convert(sourceElement, sourceType.elementTypeDescriptor(sourceElement), targetElementType);
            Array.set(array, i++, targetElement);
        }
        return array;
    }

}
